Generation of Cu nanoparticles on novel designed Fe3O4@SiO2/EP.EN.EG as reusable nanocatalyst for the reduction of nitro compounds

Article abstract of DOI:10.1039/c5ra26020e

In this work, copper nanoparticles loaded on Fe₃O₄@SiO₂, which we have named Fe₃O₄@SiO₂/EP.EN.EG@Cu for short, have been designed, prepared and characterized by XRD, FTIR, TEM, SEM, EDS, TGA, ICP, successfully. The catalytic performance was investigated in the reduction of aromatic nitro compounds in the presence of NaBH₄ aqueous solution as the source of hydrogen at 50°C. The Fe₃O₄@SiO₂/EP.EN.EG@Cu catalyst was readily removed from the reaction mixture by applying an external magnet and reused for five times without significant loss of catalytic activity.

Full text of DOI:10.1039/c5ra26020e

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Generation of Cu nanoparticles on novel designed
Fe3O4@SiO2/EP.EN.EG as reusable nanocatalyst for the reduction
of nitro compounds
Maryam Rajabzadeha, Hossein Eshghia*, Reza Khalifehb, Mehdi Bakavolia
Abstract
In this work, Copper nanoparticles loaded on Fe3O4@SiO2 which shortly named as
Fe3O4@SiO2/EP.EN.EG@Cu has been designed, prepared and characterized by XRD,
FTIR, TEM, SEM, EDS, TGA, ICP, successfully. The catalytic performance was
investigated in the reduction of aromatic nitro compounds in the presence of NaBH4
ͦ
aqueous solution as the source of hydrogen at 50 C. Fe3O4@SiO2/EP.EN.EG@Cu
catalyst was readily removed from the reaction mixture by applying an external
magnetic and reused for five times without significant loss of the catalytic activity.
Keywords:
Nanocatalyst, Fe3O4@SiO2/EP.EN.EG, Reduction, Aromatic amines
Introduction:
In the past decades, controlled assembly of nanomaterials attracted much attention. Well
known copper based catalysts in organic reactions have been given much attention by
material scientists and chemists.1ꢀ3 Homogeneous copper based catalysts have been used
in many organic transformations, but the many problems are associated with the
separation and reusability of catalyst after the reaction that prevent their industrial
applications. Therefore, the heterogenization of homogeneous catalyst to provide
supported catalysts with high active sites and high surface area became an important
protocol. Therefore, design and utilization of a heterogeneous nanocatalyst which can be
practically separated easily is desirable.4ꢀ7 Nanocatalysis has shown improved catalytic
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activity compared to bulk catalysts. This is due to an increased number of active sites for
the smaller versions of the catalysts and high surface to volume ratio as compared to
their larger counterparts.8ꢀ11 In family of nanocatalysis, the magnetic nanoparticles have
attracted increasing attention because they possess interesting properties which could see
potential use in catalysis including nanomaterialꢀbased catalysts,12 magnetic resonance
imaging,13 drug delivery systems,14 hyperthermia treatment of cancer cells.15 In addition,
magnetic nanoparticles are easily separated from the reaction mixture by an external
magnet and this is described as the more sufficient strategy than conventional techniques
such as filtration or centrifugation.16,17 Unfortunately, naked magnetic nanoparticles are
often unstable, readily aggregated and usually don’t constitute strong covalent bonds
with functionalization molecules. Encapsulation of magnetic nanoparticles in inert
matrices such as silica (SiO2) can overcome these drawbacks.18 Magnetic nanoparticles
have been extensively applied in various organic reaction, such as C–C bonding
formation,19 dihydroxylation of olefins,20 oxidation reactions21 and hydrogenation
reaction.22 Hydrogenation of nitroarene is one of the most useful methods to production
of aromatic amines. The amine group are often significant intermediates in the
fabrication of many pharmaceuticals, agrochemicals, dyes, polymers, photographic and
rubber materials.23 There are common methods to reduce a nitro precursor: metal/acid
reduction,24ꢀ26 catalytic hydrogenation,27 homogeneous catalytic transfer hydrogenation28
and heterogeneous catalytic transfer hydrogenation.29,30 However, these approaches have
several major drawbacks: metal/acid system has shown poor selectivity and this
methodology is environmentally dangerous, catalytic hydrogenation is undesirable due
to use of H2 gas at high pressure and temperature, the separation of homogeneous or
heterogeneous catalytic transfer hydrogenation, from the final product is difficult.31,32
Therefore, it is necessary to find new catalysts for hydrogenation of nitro arenes under
2

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mild conditions. In this paper we wish, to report preparation of functionalized magnetic
nanoparticles Fe3O4@SiO2/EP.EN.EG and in situ generation of Cu NPs as excellent
catalytic efficiency and the catalytic activity has been estimate by the reduction of
nitroarens to amin with NaBH4 under mild aqueous condition.
Results and discussion
As shown in Scheme 1, the Fe3O4@SiO2/EP.EN.EG@Cu nanocatalyst was prepared in 4
steps: in first step the Fe3O4@SiO2 magnetic nanoparticles was synthesized by Stöber sol–
gel method,33 in step 2, EP.EN.EG linker as novel designed ligand covalently bonded on
surface hydroxyl groups of silica coated magnetic nanoparticles. In step 3, the ligands was
activated with NaOH and then Cu(OAc)2 was complexed to this N, N, O type ligand.
Finally in step 4, Cu nanoparticles was generated with NaBH4 reduction procedure. The
synthesized Fe3O4@SiO2/EP.EN.EG@Cu was characterized by FTꢀIR, thermo gravimetric
analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy
(TEM), energy dispersive Xꢀray (EDS), Xꢀray diffraction (XRD) and vibrating sample
magnetometer (VSM).
Scheme 1 Preparation process of the Fe3O4@SiO2/EP.EN.EG@Cu
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FTIR was used to characterize the surface constructure of the synthesized materials, as
shown in Figure 1. The strong absorption bands at 573 cmꢀ1 can be attributed to the
stretching vibration of the Fe–O bond, which confirms the existence of Fe3O4. The
broad characteristic band 3444 cmꢀ1 is related to stretching vibration OꢀH,
demonstrating the presence of hydroxyl groups on the surface of Fe3O4 MNPs (Figure
1a). Comparision with Figure 1a, 1b shows, that the intensity of Fe–O bond
significantly weakens and a strong absorption peak at 1098 cmꢀ1 and weak absorption
peak at 953 cmꢀ1 was appeared. This can be assigned to asymmetric vibration of the Si–
O–Si bond and the symmetric stretching of the Si–OH bond, respectively, which
suggests that Fe3O4 was effectively coated with a silica layer. The epoxy rings which
are anchored on the surface of silica coated magnetic nanoparticles are characterized by
the methylene CꢀH stretching34 at 3050 cmꢀ1 and CꢀOꢀC vibration stretching35 at 1260ꢀ
1240 cmꢀ1. In both cases, vibration frequency was coverd by the broad band of
stretching vibration OꢀH and asymmetric vibration of the Si–O–Si bond, respectively.
The absorption bond of stretching vibration OꢀH and asymmetric vibration of the Si–
O–Si bond are getting more broadened which is clearly observed in the Figure 1c in
comparison to 1b. As shown in Figure 1d broad absorption band in the 3436 cmꢀ1 are
ascribed to the stretching vibration of OꢀH and –NH2 and the band at 3700 cmꢀ1 are due
to stretching of the NꢀH bonds or an overtone peaks of CꢀO stretching bands at 1233
cmꢀ1. Increasing of the intensity of the O–H and NꢀH stretching vibration can suggest
the attachment of the second epoxy ring to catalyst (as shown in Figure 1e).
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Figure 1 FTIR spectrum of Fe3O4(a), Fe3O4@SiO2 (b), Fe3O4@SiO2.EP (c),
Fe3O4@SiO2.EP.EN(d), Fe3O4@SiO2.EP.EN.EG (e)
The thermal stability of the Fe3O4@SiO2/EP.EN.EG was characterized by thermo
gravimetric analysis (TGA). TGA curves in Figure 2 demonstrate the weight loss
ͦ
around 100 C which was related to the loss of absorbed water molecules on the support.
ͦ
The weight loss of 13% in the temperature range of 190ꢀ600 C which was attributed to
the decomposition of organic parts that were grafted on the surface of Fe3O4@SiO2 and
amount of anchored content was evaluated to be 0.6 mmol gꢀ1. Therefore, the result
confirms that the ligand grafting had been successfully achieved.
Figure 2 TG analysis of Fe3O4@SiO2/EP.EN.EG
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The crystal structure of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2/EP.EN.EG@Cu were
characterized by XRD. As shown in Figure 3, six characteristic peaks at 2θ = 30.31,
35.64, 43.31, 53.86, 57.24, 62.83, which attributed to the (220), (311), (400), (422),
(511), (440) crystal planes confirm well with the standard Fe3O4 (cubic phase). Figure
3b Shows a new broad peak at 2θ= 23 which can be attributed to the amorphous silica
shell. Compared with curve b, we find that no remarkable change occurs in the number
of peaks in curve c, only a slight decline in the intensity of the diffraction peaks
indicating retained crystal structure of the Fe3O4 core after immobilization of Cu
nanoparticles. No peaks of Cu nanoparticles was observed in the XRD pattern due to the
disperse of Cu nanoparticles in the catalysis matrix. So, Cu nanoparticles cannot lead to
the formation of regular crystal lattice. The presence of Cu nanoparticles was verified
through the analysis of ICP and EDS techniges.
Figure 3 XRD pattern of Fe3O4 (a), Fe3O4@SiO2 (b) and Fe3O4@SiO2/EP.EN.EG@Cu
(c). Fe3O4@SiO2/EP.EN.EG@Cu catalyst after five recoveries (d).
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Figure 4a shows the SEM image of Fe3O4@SiO2/EP.EN.EG@Cu nanocatalyst. Based
on 4a spherical morphology of nanocatalyst is clearly observed. Moreover, to further
investigate the morphologies and particle size of Fe3O4@SiO2, and
Fe3O4@SiO2/EP.EN.EG@Cu, TEM images of catalyst were studied. TEM images of 4b
indicate the spherical structure of Fe3O4@SiO2 and each nanocomposite contains
several Fe3O4 nano particles in one SiO2 shell, which results in the nano composites
demonstrating strong magnetic properties.32 also the average size of MNPs is about 20
nm. As expected, the as prepared Fe3O4@SiO2/EP.EN.EG@Cu has the spherical shape
(Figure 4c), which indicates, spherical structure has not significantly influenced after
immobilization of Cu nanoparticle on the surface of Fe3O4@SiO2 support. In addition,
the attendance of Fe, Si and Cu elements are shown in EDS spectrum (Figure 4d). It also
confirmed our design to the existence of Fe3O4, SiO2 and Cu nanoelements in this
catalyst. The copper amounts of catalyst were determined by inductively coupled
plasma (ICP) 2.29 mmol gꢀ1.
4a
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4b
4c
4d
Figure 4 SEM images of Fe3O4@SiO2/EP.EN.EG@Cu (a). TEM images of the Fe3O4
@SiO2 (b). Fe3O4@SiO2/EP.EN.EG@Cu (c). EDS spectrum of the Fe3O4@SiO2/EP.
EN.EG@Cu (d).
For magnetic designed materials, the magnetic responsivity is very important.
Therefore, the magnetic properties of the Fe3O4, Fe3O4@SiO2 and
Fe3O4@SiO2/EP.EN.EG@Cu were analyzed by VSM (vibrating sample magnetometer)
at room temperature, as shown in Figure 5. As can be seen, the saturation magnetization
(Ms) value of the above magnetic samples are 63.6, 37.8 and 29.4, respectively. These
results indicated the decrease in Ms values for Fe3O4@SiO2 and
Fe3O4@SiO2/EP.EN.EG@Cu in comparison to uncoated Fe3O4. These decreases are due
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to increase in mass and size after coating the SiO2 shell and anchoring the Cu
nanoparticles. Also, in the magnetization curves no noticeable remanence or coercivity
was observed, which confirms superpara magnetic character. So, the new magnetic
materials can be easily separated by an external magnet
.
Figure 5 Magnetization curve of Fe3O4 (a), Fe3O4@SiO2 (b), Fe3O4@SiO2/EP.EN.
EG@Cu (c).
The catalytic performance of the novel Fe3O4@SiO2/EP.EN.EG@Cu as a magnetically
nanocatalyst was investigated for the reduction of aromatic nitro compounds. The
reduction reaction of paraꢀnitrophenol in the presence of NaBH4 as the source of
hydrogen (Equation I) was chosen as a model reaction to optimize the reaction
conditions. At first, the effect of solvent and molar ratio of hydrogen sources on the
model reaction were examined. (Table 1, entries1ꢀ10) It was found that water was the
best solvent for the model reaction when 3.0mmol NaBH4 as hydrogen source were used
and the product was obtained in 98% yield. (Table 1, entry 5) A rise in the amount of
NaBH4 from 0.1mmol to 3.0mmol caused increment in the rate of reduction of paraꢀ
nitrophenol (Table 1, entries 1ꢀ5). Reduction was very slow in aprotic solvents such as
THF, DMF (Table 1, entries 7ꢀ8) and nonꢀpolar solvent like toluene (Table 1, entry 10).
The employment of a protic solvents for example EtOH, CH3OH, H2O was the most
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suitable for this catalytic system (Table 1, entries 5ꢀ7), H2O was selected for the
nitroarene reduction because it is generally considered as inexpensive, safe, and
environmentally green solvent.
Table 1 Reduction of para ꢀnitrophenol in the presence of different amounts of NaBH4
in various solvents by Fe3O4@SiO2/EP.EN.EG@Cu
(Equation I)
Entry
Hydrogen source
Solvent
Time(min) Yield[%]
1
2
NaBH4 (0.1mmol)
NaBH4 (0. 5mmol)
NaBH4 (1mmol)
NaBH4 (2mmol)
NaBH4 (3mmol)
NaBH4 (3mmol)
NaBH4 (3mmol)
NaBH4 (3mmol)
NaBH4 (3mmol)
NaBH4 (3mmol)
H2O
H2O
60
60
40
40
60
90
98
95
90
20
40
20
3
H2O
45
4
H2O
45
5
H2O
15
6
EtOH
CH3OH
THF
20
7
30
8
120
120
240
9
DMF
Toluene
10
The influence of catalyst amount was investigated on the model reaction. No progress in
the reduction of aromatic nitro compounds was observed neither in the absence of
catalyst nor in the presence of Fe3O4@SiO2/EP.EN.EG. Results in Table 2 shows that,
the increasement of the amount of catalyst from 0.001 to 0.05 g per mmol of substrate,
(Table 2, entries3ꢀ7) results an increased reaction yield and the maximum yield (98%)
has been achieved in the presence of 0.05g of catalyst, (Table 2, entry 7). The results are
in good agreement with significant rise in the number of active sites.
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Table 2 Yield% dependence on the amount of Fe3O4@SiO2/EP.EN.EG@Cu
Entry
amount of catalyst (g)
Time (min)
Yield (%)
1a
2
3
4
5
6
7
ꢀ
15
15
0
Fe3O4@SiO2/EP.EN.EG
0
0.001
0.005
0.01
240
120
90
50
50
70
85
98
0.03
45
0.05
15
aIn the presence of NaBH4
As shown in Table 3, we employed the optimized conditions for the conversion of nitro
aromatic containing different functional group into the corresponding amino compounds
(Table 3, entries1ꢀ15). The results of Table 3 indicate, electron with drawing/donating
substituents do not have a remarkable influence on the reaction times and yields.
Sensitive functional groups, such as –OH, –Cl, –CH3, –COOH, –CN, –COCH3, –OCH3
and –NHCOCH3 remained intact during the reduction of nitro group (Table 3, entries 6ꢀ
14). Dinitro compounds were successfully transformed to the corresponding diamines,
which are important precursor for many heterocyclic compounds and used as a
component of engineering polymers and composites (Table 3, entries 3ꢀ5). Aldehyde
carbonyl groups in the nitro compounds were not compatible with the reaction condition
and reduction happens for both functional groups. (Table 3, entry 15). According to
steric effect that has been observed, the existence of electron with drawing/donating
groups, ortho or meta to the nitro group increased the reaction time than at the para
position. Therefore, these investigation indicated Fe3O4@SiO2/EP.EN.EG@Cu catalyst
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system was also effective for the reduction of nitro aryl compounds with high yields and
short reaction times in water.
Table 3 Reduction of various nitro aromatic compounds over Fe3O4@SiO2/
EP.EN.EG@Cu catalyst
Entry
Reactant
Product
Time(min) Yield(%)a
Mp(ºC)
ꢀ
1
15
8
85
98
2
3
4
5
100ꢀ102 ºC
(Lit. 101ꢀ104 ºC)37
10
8
98
95
100ꢀ102 ºC
(Lit. 101ꢀ104 ºC)37
64ꢀ66 ºC
(Lit. 63ꢀ65 ºC)37
5
100
139ꢀ140 ºC
(Lit. 139ꢀ141 ºC)37
6
10
95
40ꢀ41 ºC
(Lit. 40ꢀ41 ºC)38
7
10
5
95
98
57ꢀ59 ºC
(Lit. 57 ºC )39
8
62ꢀ64 ºC
(Lit. 62ꢀ66 ºC)40
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9
Immediately
100
203ꢀ205
(Lit. 203ꢀ204 ºC)41
10
11
15
20
98
90
185ꢀ187 ºC
(Lit. 187ꢀ189 ºC)42
202ꢀ204 ºC
(lit. 204ꢀ205 ºC)43
12
13
14
15
95
100
95
104ꢀ106 ºC
(Lit. 102ꢀ104 ºC)44
5
182ꢀ185 ºC
(lit. 185ꢀ186 ºC)45
5
169ꢀ170 ºC
(Lit. 172ꢀ173 ºC )45
15
Immediately
100
90ꢀ92 ºC
(Lit. 90ꢀ92 ºC)38
a) Isolated yield
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The reduction of pꢀnitrophenol to pꢀaminophenol using NaBH4 as reductant and the
Fe3O4@SiO2/EP.EN.EG@Cu as the catalyst was studied by UVꢀVis spectroscopy. The
presence of both the reactant pꢀnitrophenolate anion (λmax = 400 nm) and the product pꢀ
AP (λmax = 300 nm) can be convincingly demonstrated by the UV/Visible absorption
spectroscopy (Figure 6a). Linear relationships of ln (Ct/C0) versus reaction time was
shown in Figure 6b. Therefore, the reduction of pꢀNitrophenol follows the pseudoꢀfirst
order kinetics. The rate constant k is calculated to be 3.2 × 10ꢀ3 sꢀ1.
6a
6b
Figure
6
UV/Visible spectrum of the absorption spectra of mixture of
pꢀnitrophenol and NaBH4 in presence of Fe3O4@SiO2/EP.EN.EG@Cu at different time
(a), Plots of ln(Ct/C0) versus reaction time (b). Reaction condition: pꢀnitrophenol (5 × 10ꢀ3
ͦ
M), NaBH4 (0.5mM) and catalyst (0.08 mol%) at 50 C
The reuse ability of a catalyst is very important for a catalytic process. The
Fe3O4@SiO2/ EP.EN.EG@Cu catalyst was separated by an external magnet, was
washed with ethanol to remove the organic impurities, was dried at room temperature
and the catalyst was reused for at least 5 times. The result is presented in Table 4 and
indicates that the catalytic activity of Fe3O4@SiO2/EP.EN.EG@Cu did not decrease
after 5 consecutive cycles.
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Table 4 The catalyst reusability for the reduction of paraꢀnitrophenol
Run Time(min)
Yield(%)
1
2
3
4
5
15
15
15
15
15
98
98
98
95
95
The kinetic reusability of Fe3O4@SiO2/EP.EN.EG@Cu in the reduction of pꢀ
Nitrophenol was studied (Figure 7). Results demonstrate that
Fe3O4@SiO2/EP.EN.EG@Cu can be reused for at least 5 times. Based on these
results, the reaction was not completed even after 60 min for recycle 6. The
catalyst was recovered by an external magnetic field and then was washed with
water and ethanol to remove any absorbed products.
Figure
7
Plots of ln(Ct/C0) versus reaction time for each of
Fe3O4@SiO2/EP.EN.EG@Cu recyclability
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Comparison of TEM image, SEM image (Figure 8) of reused catalyst with fresh
catalysts (Figure 4a, 4b, 4c) showed that the morphology and structure of Fe3O4@SiO2
/EP.EN.EG@Cu catalyst was remained intact after five recoveries. The XRD pattern of
reused Fe3O4@SiO2/EP.EN.EG@Cu catalyst is shown in Figure 3d, reavled that the
Fe3O4 retain its magnetite crystalline structure after the 5 runs. In additionally, new
characteristic diffraction peaks at 2Ө= 36.88, 42.48 of Cu2O can be observed after 5
times reused of catalyst, which indicated to the reaction between small amount of Cu
nanoparticles and the air O2 due to successive performing. Furthermore, the copper
amounts of catalyst after five times reuse was determined by inductively coupled
plasma (ICP) 1.22 mmol gꢀ1.
Figure 8 TEM image of Fe3O4@SiO2/EP.EN.EG@Cu after five times reuse (a), SEM
image of Fe3O4@SiO2/EP.EN.EG@Cu after five times reuse
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The catalytic activity of Fe3O4@SiO2/EP.EN.EG@Cu was compared with various
reported catalysts in the literature46ꢀ50 in the case of reduction of 4ꢀnitrophenol. It was
observed that Fe3O4@SiO2/EP.EN. EG@Cu promotes the yield of products and reduces
the reaction time effectively in comparison with other catalysts. So,
Fe3O4@SiO2/EP.EN.EG@Cu can be considered as efficient catalyst in reduction of
nitro aryl compounds. (Table 5)
Table 5 Comparison of various catalysts for reduction of 4ꢀnitrophenol to 4ꢀ
ͦ
Entry
Catalyst
Temp(C) Time(h) Yield(%)
Ref.
1
2
3
4
5
6
CuBr2
Cu NPs
RT
50
3.5
88
66
46
47
48
49
50
5
12
Ru(0)ꢀsupported on ATꢀMont
NiCo2O4
Reflux
80
65
1.5
90
Ni/SiO2
100
50
7
100
98
Fe3O4@SiO2/EP.EN.EG@Cu
15 (min)
Present
work
aminophenol
Experimental
The melting point of the products was determined with an Electrothermal Type 9100
melting point apparatus. The FTꢀIR spectra were recorded on an Avatar 370 FTꢀIR
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Thermal Nicolet spectrometer. Mass spectra were recorded on a 5973 Network Mass
1
Selective Detector. The HNMR spectra were recorded on a Bruker AC 400 MHz
instrument in DMSOꢀd6. Termogravimetric analysis (TGA) was performed on a
Shimadzu Thermogravimetric Analyzer (TGꢀ50). Transmission electron microscope
(TEM) images were acquired on a TEM microscope Leo 912 AB120 KV Zeiss
Germany. Elemental compositions were determined with a Leo 1450 VP scanning
electron microscope equipped with an SC7620 energy dispersive spectrometer (SEMꢀ
EDS) presenting a 133 eV resolution at 20 KV. Inductively coupled plasma (ICP) was a
obtained using a Varian, VISTAꢀPRO, CCD, Australia. Xꢀray diffraction (XRD)
patterns were collected using a Braker D4 XꢀRay diffractometer with Niꢀfiltered Cu KR
radiation (40KV, 30MA). The UVꢀVis spectra were recorded on a Philips PUB 700
spectrophotometer
with a quartz cuvette (path length = 1 cm) at 50 °C.
Synthesis of Fe3O4@SiO2
The synthesis of core–shell Fe3O4@SiO2 microspheres was carried out by a Stöber sol–
gel method.29 An aqueous dispersion of Fe3O4 nanoparticles (6 ml, 0.05 g ml−1) were
dissolved into a mixture of absolute ethanol (560 ml), deionized water (140 ml).
Ammonia solution (28 wt%, 10 ml) was then added to the mixture under ultrasound for
20 min. Then, 8.0 ml tetraethyl ortosilicate (TEOS) was dropped into the mixture under
stirring for 12 h. The acquired silica coated Fe3O4 nanoparticles were separated by using
a magnet, consequently washed with ethanol several times and dried under vacuum.
General procedure for the preparation Fe3O4@SiO2/EP.EN.EP
Fe3O4@SiO2 (1 g) was added to the solution of epibromohydrin (1 ml) in ethanol (3 ml)
ͦ
and the mixture was stirred at 60 C. After 5h, the solvent was removed and the resulting
solid was washed with ethanol and dried at 80◦C. Then the dried precipitate was
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ͦ
suspended in ethylenediamine (5ml). The reaction mixture was stirred at 60 C for 24h,
after completion the product was separated by an external magnet, washed with MeOH
and dried at 80◦C, the dried powder was mixed and stirred in epibromohydrin (1 ml) and
ͦ
ethanol (3 ml) at 60 C for 5h, the resulting solid material was separated by an external
magnet, washed with MeOH and dried at 80◦C.
General procedure for the preparation of copper nanoparticles loaded on magnetic
core (Fe3O4@SiO2/EP.EN.EG@Cu)
In first step, Fe3O4@SiO2/EP.EN.EP (0.5 gr) was activated at room temperature for 1h
in the presence of 5ml NaOH solution(0.1 mol L−1), after separation, the activated
catalyst (Fe3O4@SiO2/EP.EN.EG) washed with water and ethanol several times. In
second step, Cu(OAc)2 (0.25 gr) dissolved in absolute EtOH (5 ml) and stirred at room
temperature for 4h with 0.5 gr activated catalyst. Then, solution of sodium borohydride
(10.0 ml, 0.15 mol L−1) was added dropwise to the mixture and stirred under Ar
atmospher for 2 h. Finally, nanocatalyst collected by magnetic separation, washed with
MeOH and dried under vacuum at room temperature for 8h.
General procedure for reduction of nitro compounds in the presence of
Fe3O4@SiO2/EP.EN.EG@Cu
Suspension of NaBH4 (3 mmol) in H2O (3 ml) was added to nitro compound (1 mmol),
ͦ
then stirred at 50 C in presence of Fe3O4@SiO2/EP.EN.EG@Cu (0.05gr) in water. The
reaction progress was monitored by TLC, after the completion of the reaction the
catalyst was taken out with external magnet and washed with ethanol. The reaction
mixture was extracted with ethyl acetate and the combined organic layer was dried with
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Na2SO4. The product was purified by column chromatography by using hexaneꢀethyl
acetate as solvent system in different concentration to obtain the pure compound.
p-Toluidine (Table 3, Entry 6): FTꢀIR (KBr, cmꢀ1): 3417, 3336, 3220, 3009, 2913,
1
2859, 1623, 1515, 1268, 1176, 813. H NMR (400 MHz, DMSOꢀd6): 6.83 (d,
J = 12
Hz, 2H, Ph), 6.49(d,
m/z (%) 107 [M+].
J = 12 Hz, 2H, Ph), 4.78(s, 2H, NH2), 2.14 (s, 3H, Me). MS (EI):
N,N'-(4-amino-1,2-phenylene)diacetamide (Table 3, Entry 11): FTꢀIR (KBr, cmꢀ1):
1
3395, 3331, 3227, 3056, 1654, 1590, 1511, 1438, 1360, 1281. H NMR (400 MHz,
DMSOꢀd6): 9.22 (s, 2H, NH), 8.26ꢀ8.23 (m, 1H, Ph), 7.85 (dd,
J = 12 Hz, J = 3.2 Hz,
1H, Ph), 6.74 (d, = 12 Hz , 1H, Ph) ,6.51 (s, 2H, NH2), 2.08 (s, 3H, Me).
J
4-amin acetophenon (Table 3, Entry 12): FTꢀIR (KBr, cmꢀ1): 3395, 3331, 3227, 3056,
1
1654, 1590, 1511, 1438, 1360, 1281. H NMR (400 MHz, DMSOꢀd6): 7.67 (d,
J = 12
Hz, 2H, Ph), 6.56 (d,
m/z (%) 135 [M+].
J = 12 Hz, 2H, Ph), 6.04 (s, 2H, NH2), 2.39 (s, 3H, Me). MS (EI):
4-Aminobenzoic acid (Table 3, Entry 13): FTꢀIR (KBr, cmꢀ1): 3460, 3381, 3363, 3235,
2978, 2823, 2671, 2594, 1665, 1624, 1600, 1572, 1442, 1421, 1312, 1291. 1H NMR(400
MHz, DMSOꢀd6): 12.0(br, 1H, OH), 7.62(d,
J = 12 Hz, 2H, Ph), 6.54(d, J = 8 Hz, 2H,
Ph), 5.88(s, 2H, NH2). MS (EI): m/z (%) 137[M+].
Conclusion
In summary, we report the preparation and characterization of novel designed
Fe3O4@SiO2/EP.EN.EG@Cu catalyst. This catalyst demonstrate excellent catalytic
performance in reduction of aromatic nitro compounds. The advantages of this catalytic
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system are: (a) ease of preparation, use and separation of catalyst (b) the mild reaction
conditions, (c) short reaction times and (d) high yields of substituted amines.
Notes and references
ªDepartment of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran.
bDepartment of Chemistry, Shiraz University of Technology, Shiraz, 71555-313,Shiraz, Iran.
* Corresponding author: E-mail: heshghi@ferdowsi.um.ac.ir
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Generation of Cu nanoparticles on novel
designed Fe3O4@SiO2/EP.EN.EG as
reusable nanocatalyst for the reduction of
nitro compounds
Maryam Rajabzadeha, Hossein Eshghia*,
Reza Khalifehb, Mehdi Bakavolia,
1. Reusable magnetic Cu nanocatalyst was
designed and characterized
2. An efficient and mild method for the
reduction of aromatic nitro compounds
Graphical Abstract